People inspect the site of a car bomb attack on cars lined up at a gas station in the oil rich city of Kirkuk, in northern Iraq, Thursday. The lightning sweep by the militants over much of northern and western Iraq the past month has dramatically hiked tensions between the country’s Shiite majority and Sunni minority. At the same time, splits have grown between the Shiite-led government in Baghdad and the Kurdish autonomous region in the north.

BAGHDAD — Kurdish security forces took over two major oil fields outside the disputed northern city of Kirkuk before dawn Friday and said they would use some of the production for domestic purposes, further widening a split with the central government of Prime Minister Nouri al-Maliki.

The takeover of the Bai Hassan and Kirkuk oil fields were the latest land grabs by Kurds, who have responded to the Sunni militant insurgency that has overrun large parts of Iraq by seizing territory of their own, effectively expanding the Kurdish autonomous zone in the north. Those moves have infuriated al-Maliki’s government while stoking independence sentiment among the Kurds.

Kurdish fighters known as peshmerga pushed into the city of Kirkuk, a major hub for the oil industry in the north, and the surrounding area weeks ago in the early days of the Sunni militant blitz. But until now they had not moved into the oil fields in the area. On Friday, however, the fighters took over the Bai Hassan and Kirkuk fields and expelled local workers, the Oil Ministry in Baghdad said.

Oil Ministry spokesman Assem Jihad denounced the move as “a violation to the constitution” and warned that it poses “a threat to national unity.”

The Kurdish Regional Government said its forces moved to secure the fields after learning of what it said were orders by officials in the Oil Ministry to sabotage a pipeline linking oil facilities in the area. It said production would continue, and that staff can return but will operate under Kurdish management.

Production from the fields will be used to fill the shortage of refined products in the domestic market, it said, in a reference to a fuel crunch in the Kurdish region. It also said the Kurdish Regional Government will claim its “constitutional share” of revenues from the fields to compensate for Baghdad’s cutting off the 17 percent of the state budget — some $20 billion in this year’s projected budget — that is supposed to be given to the Kurdish region.

The central government withheld the funds after the Kurds began moving oil from fields inside the autonomous zone to Turkey independently against Baghdad’s wishes.

The Kurds have said their earlier moves into disputed lands were intended to protect the areas from Sunni militants after the collapse of the Iraqi military in the face of the insurgency the past month. But the territory they seized has large Kurdish communities and has long been claimed by the autonomy zone.

In past weeks, the president of the Kurdish zone has said the areas won’t be returned — including the highly disputed, flashpoint city of Kirkuk — and he called for Kurdish lawmakers to prepare to hold an independence referendum in the area, a move strongly opposed by Baghdad and the United States. Sunni Arabs and ethnic Turkmens who also claim Kirkuk as theirs have warned of a backlash if Kurds try to monopolize the oil in the region.

The Kurds and Baghdad have feuded for years over oil resources, disputed territory and a host of other issues. Yet, they have also found room for compromise, and the Kurds have provided critical backing to help al-Maliki become prime minister.

But their ties are rapidly unraveling as the country fragments in the face of the Sunni militant blitz, led by the Islamic State extremist group. The country is effectively being cleaved along ethnic and sectarian lines — the swath of militant-held Sunni areas, the Shiite-majority south and center ruled by the Shiite-led government in Baghdad and the Kurdish north.

The conflict has also fueled fears of sectarian bloodshed between Shiites and Sunnis. On Friday, Human Rights Watch said Iraqi security forces and government-affiliated militias appear to have killed at least 255 prisoners in six cities and villages since June 9.